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Thread: Valve shims

  1. #1
    CB750 Enthusiast Windy's Avatar
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    Valve shims

    Morning all, Iím in the UK & was wondering where people buy valve shins from, how much they are & which are the common sizes to buy?
    Cheers people.

  2. #2
    CB750 Guru amc49's Avatar
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    Over here stateside K&L Supply sells them. roughly $5 each and no way to guess at what sizes as every bike is different. You have to measure before any clue.

  3. #3
    CB750 Enthusiast Windy's Avatar
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    Thanks for the reply. My clearances are as follows:-
    Inlets 4 4, 4 4, 2 1, 4 4
    Exhaust 1 4, 4 4, 4 4, 2 2
    All measured in thousandth of an inch.
    Do I take each one out, calculate what I need then put it back before moving on to the next one? Then order what I need & go back again to fit the new shims. Canít see another way.
    Any advice? Cheers

  4. #4
    CB750 Guru amc49's Avatar
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    You got it right.

    The 4s are all OK, the 2s and lower definitely need fixing, they will burn valves.

    Gonna rock your world maybe. Do NOT use the factory service manual number of .003" as the go to number, use .005". The engine will absolutely love you for it. Meaning use .004"-.006" as your range rather than .002"-.004". Making many of yours perfect.

    The cams move around in more looseness than the valves do (check the OEM clearances there to verify it) and that allows the fairly strong valve springs to push the cams around in the cap looseness to give you somewhat fake valve clearance numbers. They are tighter when running than what you get measuring and about .002" or so of clearance you think you have is not really there when bike is running. One big reason why the valves have to set so much, loosen up a bit and they can go 20K miles with no burning issues BTDT. Too tight also wipes the cam lobes of oil at .002" and less and one reason why the bigger DOHC engines wipe out cams so quickly, it being very hard to find a good set with no dead lobes on them. Honda was somewhat aware of the issue as they did a cheapie setting marks change in '82 when they realized the clearances were not accurate but nothing more as the engine type was being dumped for the V4 at the time.

  5. #5
    CB750 Guru amc49's Avatar
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    Whatever you do, do NOT turn the engine at all with a shim removed, it will lead to damage.

  6. #6
    CB750 Addict Dave's Avatar
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    Quote Originally Posted by Windy View Post
    Do I take each one out, calculate what I need then put it back before moving on to the next one? Then order what I need & go back again to fit the new shims. Can’t see another way.
    Any advice? Cheers
    Yup! and mic them where the cam wears on them, don't trust the markings.
    96% of the time I edit my replies so check back for updates if it isn't at least an hour old

  7. #7
    CB750 Enthusiast Windy's Avatar
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    Thanks guys, the wealth of knowledge on this forum is amazing!! It was only by reading comments on here (mainly from AMC49) that I even thought about valve timing. I made the mistake of blaming the carbs for it running like s**t. Mind you, Iím used to Amal carbs & ohv engines!!
    Just thinking, would it be easier to work out clearances in metric rather than imperial??
    Whatís your thoughts.
    Cheers

  8. #8
    CB750 Addict Chris in Dorset England's Avatar
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    Quote Originally Posted by Windy View Post
    Morning all, I’m in the UK & was wondering where people buy valve shins from, how much they are & which are the common sizes to buy?
    Cheers people.
    David Silver Spares near Saxmunden not far from you

  9. #9
    CB750 Enthusiast Windy's Avatar
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    Thanks Chris, do you measure & calculate clearances/shims in metricvor imperial?
    Cheers Windy

  10. #10
    CB750 Guru amc49's Avatar
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    I'm not 100% clear on what 'imperial' entails but if in thousandths then it is the same as what we call SAE (Society of Automotive Engineers set the standards there) here. Either one is often whatever the owner is most comfortable with. I grew up with Japanese bikes of the '60s and can easily switch from one to the other. Thinking the bikes are actually ISO metric (International Standards Organization).

    X2, David Silver will have access to them.

    Put any shims back in with the number facing down to preserve it, handy when you want to calculate possible wear, but commonly the shims only polish with no wear to speak of unless in the motor for a long time. Something else to consider is that any engine on the planet generally does not like the parts that run on cam lobes changed, it can lead to accelerated wear. Not really a problem on these but give some thought to any shim that seems to have wear beyond just a polish, changing it may well kill a cam lobe as the lobe will likely be just as worn as the shim, and changing the shim on that one is often just what is needed to make the parts suddenly go wild with wear. If the wear on shim begins to show a circle I often use it in another position flipped to use the non-worn side to at least have one part be dimensionally correct. In that case I sacrifice the printed number for something of more value, the flat. 750s have no cam lift to speak of and for that reason the cams hold up much better than say 900 or 1100 ones. All are surface nitrided only as a heat treat and it varies in depth but usually no more than .005"-.010" max thick. The bigger engines have more lift and the cams tend to wear more with the 1100 ones wearing often like lightning. Why the bigger one goes looking to use them for high-perf the harder they are to find in good shape.

  11. #11
    CB750 Enthusiast Windy's Avatar
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    Thanks amc. When Iíve done the calculations, Iíll post them on here for you to double check before Iborer replacements, if youíll be so kind?
    You really have a wealth of knowledge that is astounding!!
    This is my first foray into a CB750 & this forum is invaluable.
    Thanks again.
    Cheers

  12. #12
    CB750 Addict Chris in Dorset England's Avatar
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    Quote Originally Posted by Windy View Post
    Thanks Chris, do you measure & calculate clearances/shims in metricvor imperial?
    Cheers Windy
    I keep with metric, the shims are metric too, saves faffing about with conversions.

  13. #13
    CB750 Enthusiast Windy's Avatar
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    Ok, Iíve had the shims out relating to the tight valve clearances, measured them & used an online shim calculator & this is what Iíve come up with. Can anyone check these figures for me before I order new shims? This is using .006 thou as the clearance needed.

    Measured clearance .001 thou
    Existing shim size. 3.33mm
    Shim needed 3.2mm

    Measured clearance .002thou
    Existing shim size. 2.76mm
    Shim needed. 2.66

    Measured clearance. .003 thou
    Existing shim size. 2.65mm
    Shim needed. 2.57mm

    Measured clearance. .002 thou
    Existing shim size. 2.50mm
    Shim needed. 2.40mm

    Measured clearance. .001 thou
    Existing shim size. 2.55mm
    Shim needed. 2.42mm

    What do you think guys?
    Cheers Windy

  14. #14
    CB750 Guru amc49's Avatar
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    Use .005" not .006".............The shims come in .05 mm., or same as .002" SAE. You will find some like the 2.76 that are custom close set shims only available to the engine builder when the engines were built, they are not available except maybe in a dealer parts bin as leftovers from back in the days.

    In the order posted there and needed (1) 3.20, (2) 2.65, (3) 2.60, (4) 2.40, (5) 2.45 or a 2.40 works fine too. I tend to err on the loose side as the valves tend to get closer with wear, the valve seat wears faster than the tips to let the valve generally sink deeper in the hole (it goes UP on these).

    Getting kind of close, the shim range ends at 2.30 and always an issue with these DOHC as they get older. Some people have figured out ways to shave the shims thinner, I myself tend to ground the valve tip down a bit with engine apart for work if I know a few are getting too high, and the tappet has a little bump on it that can be modded too.

  15. #15
    CB750 Addict Wez_'s Avatar
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    It really helps if you have squishy springs or the inner spring removed when shimming. I didn't learn this until later in the game. I was installing and removing the cam under full spring pressure each and every time to get the shim clearance correct. AMC suggested soft springs or removing the inner spring for easier installation and clearance measurements. Great advice. Also, both the inner and outer springs are directional and need to be installed in the correct orientation.

    Lastly, don't forget to play "musical shims". It's a fun game to play

    But honestly, it will save you money.

    Take a look at your numbers. # 3 shim (2.65) will likely work for # 2 (2.66 needed)

    Also, # 5 (2.55) will likely work for # 3 (2.57 needed)

    Money saved.

    Also, do the measurements multiple times for accuracy as I noticed the numbers varied until I repeated the cam/caps installation and torque the same way each and every time. Don't short cut installing or torqueing the caps as it will effect this tiny clearance. Each and every time you seat the cam go through all the factory checks like tachometer gear alignment and there is a bearing cap with a shoulder cut into it. You are supposed to push the cam up against it for alignment when installing the cam otherwise binding occurs which I think might effect the numbers. I may be wrong but at the very least its good practice to prepare you for the final install ahead and you want repeatable measurements which come from a consistent installation and measurement procedure. Be systematic. I wasn't satisfied until I installed both sprockets, chains and cam/caps.
    Last edited by Wez_; 03-26-2018 at 11:57 AM.

  16. #16
    CB750 Enthusiast Windy's Avatar
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    Great advice Wes. Youíre right, musical shims is a fun way to while away those long dark evenings!!😖

  17. #17
    CB750 Guru amc49's Avatar
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    'Also, do the measurements multiple times for accuracy as I noticed the numbers varied...'

    They will vary anyway if you are looking CLOSE, the problem I refer to. You can line the marks or lobes up 5 times and get slightly different clearance every time, the cams are moving around in the cam clearance based on the spring load. The cam clearance is whoppingly bigger than the valve clearance. Give that some thought. Normal engines do not do that, the valve clearance is much larger and zero issues then. The race guys sand the cam caps to hit .002" all the way down, the Honda numbers? Look at the service manual, each one is different. Whacky. They get looser toward the middle, I'm thinking Honda was scared the engines would tighten up when they got hot to seize at the middle.

    The light setting springs I refer to are for head OFF OF ENGINE ONLY. You must use a special tool to set each pair of spring/valve assemblies to pull shims. Tool goes in between valve pairs and engine then rotated by hand to push valves down, then the tool holds them down in place while cam lobes are backed away (easy to bend valves doing it, consider the opposing pair!) and then easy to use say tweezers to pull shims out.

    https://www.denniskirk.com/motion-pr....prd/28268.sku

    I remember when that tool only came from Honda and at $80 each..........

    Yes, on #3 using the reject shim from #5, I missed that. Always reuse when you can if the shim surface is still smooth.
    Last edited by amc49; 03-28-2018 at 05:17 AM.

  18. #18
    CB750 Enthusiast Windy's Avatar
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    Hi all, thanks for all the replies. Just to let you know Iíve sorted the valve timing out & have 4thou on all 16 valves now!! I did a compression test yesterday & got 135 on all 4 cylinders, before I did the valves #3 was 105 (obviously valves being held open) . Just got the carbs to sort now. Gonna put a post in the carb section so feel free to reply. Cheers you lot, youíre ACE!! Windy

  19. #19
    CB750 Enthusiast Oliver Boy's Avatar
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    Deleted entry, answered my own silly question
    Last edited by Oliver Boy; 07-27-2018 at 11:51 PM. Reason: Answered my own silly question :) no response required

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